The present invention is concerned with the reliable detection of measurement quantities from a given process and the forwarding thereof to a superordinate system for an arbitrary application. FIG. 10 shows a schematic diagram of a data acquisition system in accordance with the prior art, which may also be referred to as a sensor. The data acquisition system is designated in its entirety by 1000. In this case, the data acquisition system 1000 comprises a process 1010 to be monitored. A sensor element 1020 detects a measurement quantity 1024 of the process 1010 to be monitored. The sensor element 1020 furthermore forwards one or more electrical quantities 1028 to a data conditioning 1030. The data conditioning 1030 generates measurement data 1034 based on the at least one electrical quantity 1028 and forwards said measurement data to an interface 1040. The interface 1040 conditions the measurement data 1034 for further processing by a superordinate arrangement (not shown here). The forwarding of the data from the interface 1040 to the superordinate arrangement is indicated by an arrow 1050.
It should be pointed out in this case that different types of sensors are used in practice. Thus, there are sensors with an external sensor element, in the case of which the sensor element 1020 is separate from the data conditioning 1030 and the interface 1040. By way of example, the sensor element 1020 may be arranged spatially separate from the data conditioning 1030 and the interface 1040. On the other hand, sensors with an integrated sensor element are also customary, sensor element, data conditioning and interface being regarded as one unit (as the sensor). By way of example, it is possible for the sensor element 1020, the data conditioning 1030 and the interface 1040 to be monolithically integrated.
In the system under consideration (the data acquisition system 1000), the sensor element 1020 can detect an arbitrary measurement quantity 1024 from the given process 1010—directly or indirectly, actively or passively. It is pointed out, moreover, that the sensor element 1020 can of course also detect a plurality of arbitrary measurement quantities 1024. In general, the resulting quantities are available as electrical signals or electrical quantities 1028 for further processing in the data conditioning 1030.
In integrated sensor systems, but perfectly well in discretely constructed systems, too, the three function blocks sensor element 1020, data conditioning 1030 and interface 1040 may be regarded as a common unit—the “sensor”.
However, systems also exist which have jointly operated data conditioning 1030 and interface 1040, which acquire electrical quantities 1028 from an external sensor element 1020 and thus form a sensor-data conditioning system.
Irrespective of whether the sensor element is fixedly connected to the data conditioning 1030 and the interface 1040, the expression “sensor” is used in this case for all the possibilities described in the rest of the description. In other words, the expression “sensor” designates for example the combination of a sensor element 1020 with a data conditioning 1030 and an interface 1040. Equally, the expression “sensor” designates the combination of a data conditioning 1030 for a sensor element in conjunction with a suitable interface 1040 even when the sensor element 1020 is indeed not coupled to the data conditioning 1030, or obtains the electrical quantities or measurement data in turn from an upstream data processing unit.
It may thus be emphasized that hereinafter systems which have jointly operated data conditioning and interface which acquire electrical quantities from an external sensor element (for instance in the form of a sensor-data conditioning system) are also designated as sensor. In other words, generally referring to the possibility described here, the expression “sensor” is quite generally used hereinafter.
The behaviour of a sensor taking account of interference influences is of crucial importance in application technology. Ideally, even given the presence of an external disturbance which may be caused for example by an electromagnetic coupling, a problem of electromagnetic compatibility (EMC) or by a supply voltage dip, a sensor should forward correct measurement data to the superordinate system without any impairment.
It is advantageous if a sensor can at least identify a disturbance. Thus, sensors are often equipped with monitoring circuits in order to indicate a possible error behaviour to a superordinate system to which the respective sensor is coupled. By way of example, a sensor may concomitantly measure its own supply voltage and forward a signal in the event of limit values being exceeded or undershot. This functionality is often referred to as “overvoltage/undervoltage detect”.
The problem in conventional sensor systems is that a disturbance can influence the evaluation circuit (data conditioning 1030) and the interface circuit (interface 1040) insofar as a reinitialization or a time-intensive normalization of the sensor data are required. During the reinitialization or the time-intensive normalization, the sensor data or output data supplied to the superordinate system are no longer valid and therefore also unusable for a specific time. By way of example, the output data, on account of an internal low-pass filter behaviour after a disturbance or a reinitialization or normalization of the sensor data, must first return to an initial situation again. In other words, the sensor must first settle again after a disturbance.
FIG. 11 shows a schematic illustration of a simple sensor system having three terminals. The sensor system shown in FIG. 11 is designated in its entirety by 1100. The heart of the sensor system 1100 is a sensor 1110. The sensor 1110 is designed to detect a measurement quantity 1120. Furthermore, the sensor 1110 is coupled to a reference potential GND and a supply potential 1130 for voltage supply purposes. Output data 1144 are present at an output 1140 of the sensor 1110. The output data 1144 are based on the measurement quantity 1120 and are furthermore dependent on the voltage supply of the sensor 1110, that is to say a voltage between the supply potential 1130 and the reference potential GND.
FIG. 12 shows a graphical illustration of the output data of exemplary sensor systems in accordance with the prior art as a response to a disturbance of the voltage supply. The graphical illustration of FIG. 12 is designated in its entirety by 1200. A first temporal illustration 1210 describes the supply voltage that supplies the sensor 1110, as a function of time. Consequently, the time is plotted on an abscissa 1212. An ordinate 1214 shows the supply voltage of the sensor 1110, that is to say the difference between the supply potential 1130 and the reference potential GND. A first curve 1216 describes a temporal profile of the supply voltage. The first temporal illustration 1212 furthermore shows a dip 1218 in the supply voltage, which represents a disturbance of the voltage supply.
A second temporal illustration 1230 describes the output data 1144 of an exemplary sensor 1110 as a function of time. The second temporal illustration 1230 consequently shows a first possible reaction of an exemplary sensor 1110. An abscissa 1232 of the second temporal illustration 1230 once again describes the time. An ordinate 1234 furthermore describes the output data 1144 of an exemplary sensor 1110. A second curve 1236 describes a temporal profile of the output data 1144 at the output 1140 of the exemplary sensor 1110. Reference is made here to the fact that the output data 1144 may be present as an analogue signal or as a digital signal. The second temporal illustration 1230 shows the magnitude of such an output signal. It can be discerned from the second temporal illustration 1230 that the output data shown by the second curve 1236 have a dip 1238 that is effected approximately at the same time as the dip 1218 in the supply voltage as shown in the first temporal illustration. Furthermore, the second temporal illustration 1230 shows a start-up 1240 of the output data 1144 of the exemplary sensor 1110. In other words, after the dip 1238 in the output data 1144, the output data assume a high value again, which is approximately equal to the value of the output data prior to the dip 1238, only for a short time before thereupon returning to zero. During the start-up 1240, the output data 1144 then slowly move back to an original value that was present prior to the dip 1238.
A third temporal illustration 1250 shows a further exemplary profile of the output data 1144 of an exemplary sensor 1110. In other words, the third temporal illustration 1250 describes a second possible reaction of an exemplary sensor 1110 to a dip 1218 in the voltage supply. An abscissa 1252 of the third temporal illustration 1250 again describes the time. By contrast, an ordinate 1254 of the third temporal illustration 1250 shows the output data 1144 of the exemplary sensor 1110. A third curve 1256 describes the temporal profile of the output data.
The third curve 1256 shows a dip 1258 in the output data which takes place approximately at the same time as the dip 1218 in the supply voltage. Shortly after the dip 1258 in the output data 1144, the output data again assume the value prior to the dip 1258. However, an attenuated-oscillating start-up 1260 follows, during which the output data 1144 oscillate about the final value. A constant final value is then assumed again after a specific time duration.
In other words, the graphical illustration 1200 shows two possible behaviours of sensors with an output voltage that is ratiometric with respect to the supply on account of a supply voltage dip 1218.
In both cases shown in the second temporal illustration 1230 and the third temporal illustration 1250, the output data (or the output) firstly follow the dip 1218 in the supply voltage. This is to be expected since a ratiometric sensor is assumed here, in the case of which the output voltage for a fixed value of the measurement quantity 1120 is proportional to the supply voltage. In both cases shown, internal function blocks of the sensor have to be reinitialized as a safety feature since the dip 1218 in the supply voltage is so great that this could lead to functional inconsistencies. Especially if a sensor or sensor system may only be equipped with few control lines, it may be problematic to forward this state (that is to say the reinitialization of the function blocks) towards the outside.
In the case of the first reaction shown in the second temporal illustration 1230, a restart (or a reinitialization of the function blocks of the sensor) is followed by a visible start-up 1240 of the output voltage that is illustrated by the second curve 1236. It should be noted here that the output voltage essentially corresponds to the output data. As shown in the third temporal illustration 1250, an attenuated-oscillating start-up 1260 may also follow in the case of a second possible reaction of the output data (output voltage) as a reaction to a disturbance (dip) of the voltage supply in the case of a restart (reinitialization of the function blocks of the sensor). The type of behaviour after the restart or the reinitialization of the function blocks of the sensor generally depends on the underlying function and conception of the sensor system. Consequently, the behaviours described are also to be regarded only by way of example; arbitrary other signal shapes between the disturbance and the recovered state are also conceivable on account of the diverse possibilities of the detailed construction of a sensor system.
Furthermore, it should be noted that the frequency of digital signal evaluation is increasing precisely in modern sensor systems. This is because a digital signal evaluation affords at least two important advantages. Thus, a digital signal evaluation enables a deterministic processing of implemented algorithms and methods. Furthermore, a digital signal evaluation opens up an efficient and simple possibility for testing the corresponding function blocks at the end of a production line.
However, digital circuits are difficult to assess in terms of their interference behaviour with regard to diverse disturbances. Equally, measures for eliminating the problems described can be assessed only with difficulty in the case of digital circuits.
Known measures for improving the behaviour of sensors given the presence of external disturbances are described briefly below. The most important and best means for minimizing the problem of interference influencing has hitherto been to make a sensor system itself robust by providing a stable voltage supply and through suitable measures for interference filtering in order to keep the thresholds for the identification and triggering of a reaction to a disturbance, that is to say e.g. a start-up or reinitialization of function blocks of the sensor, as low as possible.
Furthermore, it is possible to make the start-up as short as possible by means of suitable techniques. In analogue circuit technology, attempts may also be made to buffer voltages (and if appropriate currents) to an extent such that a completely new start-up is prevented.
However, it should be pointed out that especially when using digital evaluation methods, digital filters and similar digital circuits, a sufficiently disturbance-immune design has not been possible hitherto, which makes a complete start-up essential in the case of disturbance. This is because a voltage dip during a clock edge of a digital system may lead to unforeseeable reaction. By way of example, counters may miscount. Moreover, data may be stored incompletely in the event of a disturbance of a digital circuit.
The abovementioned measures for improving the interference immunity of sensors therefore do not permit a complete suppression of disturbances to be realized. Rather, in conventional sensors there are a multiplicity of cases of interference which do not satisfy the desire for total suppression of interference events.